Infinite positioning mechanism for a movable arm



A ril 1, 1969 F- 3,436,046

INFINITE POSITIONING MECHANISM FDR A MOVABLE ARM Filed Sept. 1, 1967 7 JI I 6285 63- 6-1 I INVENTOR.

JOHN J. VALESKA ATTORNEY States ABSTRACT OF THE DISCLOSURE A movablearm, for use in combination with a dental console, supports aninstrument tray outwardly spaced from the console. The arm, movable inboth horizontal and vertical planes carries a friction lock, whichpermits free upward movement of the arm but locks instantly when theupward movement is stopped and the arm begins to fall by gravity. Thelock has a manual release for disengaging the lock to move the arm to alower level. The lock is operable over the entire range of verticalmovement of the arm so that the arm can be positioned at any pointwithin the range of vertical movement.

The present invention relates to a movable arm for supporting a platformoutwardly spaced from an upright structure, and more specifically tosuch an arm as may be attached to a dental console to hold an instrumenttray within reach of the dentist. In particular, the invention relatesto an arm of the type described having a lock mechanism whichautomatically locks whenever the arm is subjected to the force ofgravity and automatically unlocks Whenever upward pressure is applied tothe arm.

Movable arm supports for dental consoles are well known in the art.These arms are usually hinged and pivoted to the console so that the armcan swing in both vertical and horizontal planes. The arm usuallycarries at its outer limit some sort of platform or tray on which thedentist can place, within easy reach, his picks, mirrors or otherhandtools, extra burrs for the power operated drills, materials formixing the amalgam fillings and other small items. The flexibility ofthe arm permits the tray to swing over the patient to the position mostconvenient to the dentist.

The movable arms in the prior art lock against downward movement atseveral ditferent heights so that the instrument tray will be reasonablyclose to the patient and within reach of the dentist regardless ofwhether the patient is seated upright or reclining. However, severaldrawbacks inherent in prior art arm members can be attributed to theconstruction of the locking mechanism used to hold the arm at differentlevels. For example, the locking mechanisms are designed to lock atseveral set intervals so that the instrument tray could be positionedonly at a limited number of vertical height positions. These locks arealso designed to hold the arm in position against both upward anddownward movement. In such a case, the dentist must be sure to raise orpivot the arm away from the patient before elevating him. Otherwise thepatient might become jammed against the unyielding arm as he is elevatedin the dental chair causing possible injury to both the patient and thearm.

Other movable arms which yield upwardly to safeguard equipment andpatient return to the original lock position when released. With thistype of arm the dentist must reset the locking mechanism each time hewishes to reposition the arm at a higher level.

atent O Patented Apr. 1, 1 969 SUMMARY OF THE INVENTION In the presentinvention a friction lock is adapted to lock automatically wheneverdownward pressure is exerted on the movable arm, which prevents the armfrom lowering and to unlock automatically to permit free unimpededmovement of the arm under the influence of an upwardly directed force.To this end, the movable arm comprises a parallel motion linkage whereinthe parallel members move axially, one relative to another, when the armis raised or lowered. A plurality of locking discs and a latch slidablycarried by one of the parallel members are springurged against a stopcarried by the other parallel member, the stop being set at an angle totilt the locking discs and the latch which in turn binds and preventsthe relative axial motion of the parallel members when the membersattempt to move downwardly. Applying upper pressure to the parallelmembers to move the members upwardly, carries the locking discs andlatch away from the stop and permits the parallel members to moveupwardly.

Since there are no ratchets or stations to engage, the friction lockalso has the advantage of locking the arm at an infinite number oflevels over the entire vertical movement range of the arm. This featureallows the dentist to position the arm and tray at the level mostconvenient for the performance of his work.

Accordingly, it is an object of my invention to provide a movable armfor dental units and the like which will lock the arm at any level overthe entire vertical range of arm movement to permit the dentist toposition the instrument tray at the most convenient level.

Another object of my invention is to provide a lock mechanism incombination with a movable arm of the type described which locks onlywhen the arm is subjected to downward pressure.

Still another object of my invention is to provide a locking mechanismin combination with an arm for dental units and the like which willprevent injury to the patient or to the arm itself resulting from thepatient being jammed upwardly against the arm.

A further object of my invention is to provide a movable arm for dentalunits and the like which can be raised without disengaging the lockmechanism.

These and other objects, advantages, and characterizing features of myinvention will become more apparent upon consideration of the followingdetailed description thereof when taken in conjunction with theaccompanying drawings depicting the same in which:

FIGURE 1 is an elevation view of the movable arm assembly of myinvention with the phantom line representing the upper limit of verticalmovement and the solid line representing the lower limit of verticalmovement; and

FIGURE 2 is an enlarged cross sectional view of the lock mechanism of myinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT My invention can becharacterized in one aspect thereof by the provision of a movable armhaving a pair of elongated parallel members pivotally supported at oneend and pivotally connected to a platform at their other end, themembers being adapted to move axially one relative to another as theyare pivoted vertically about the pivotally supported end. One of theparallel members slidably carries a friction lock and the other membercarries a stop. The friction lock is adapted to engage the stop toprevent the members from moving axially one relative to the other as theparallel members attempt to pivot downwardly about the pivotallysupported end to prevent downward movement of the arm. The lock is,

however, carried away from the stop when upward pressure is applied tothe arm so that the arm can be moved upwardly.

Referring now to the drawings, FIGURE 1 shows the arm assembly and thelock mechanism of my invention generally designated at 10. The armassembly includes a pair of parallel members 12 and 14, both pivotallysupported at one end by a pivot member 16 and pivotally connected attheir other end to a knuckle 18. Pivot member 16 in turn connects thearm assembly to a dental console 20 and knuckle 18 connects the armassembly to an instrument tray 22 on which the dentist places his handtools and other like equipment. The pivot action of pivot member 16 andknuckle 18 permits the instrument tray to swing in both a horizontal orvertical plane over the seated or reclining patient.

Member 12 is generally U-shaped in cross section and forms a casing formember 14, the member 14 being disposed entirely within member 12 asshown in FIGURES 1 and 2. Members 12 and 14 together define a parallelmotion linkage which in and of itself is well known and old in the art.Since parallel motion linkages are well known in the art, the operationof such a linkage will be described only briefly to clarify the presentinvention.

In order for the parallel motion linkage to function it is essentialthat the distance between the points of connection of member 12 to pivot16 and knuckle 18 is substantially equal to the distance between thepoints of connection of member 14 to pivot 16 and knuckle 18. With thisarrangement, pivoting parallel members 12 and 14 downwardly about pivotmember 16 causes the parallel members to move axially one relative toanother as indicated by arrows 26 in FIGURE 1. In like respect pivotingparallel members 12 and 14 upwardly about pivot member 16 causes theparallel members to move axially one relative to another as indicated byarrows 28 in FIG- URE 1. The relative axial movement of the parallelmembers acts to maintain knuckle 18 and thereby instrument tray 22 in asubstantially level position regardless of the inclination of members 12and 14 as the arm assembly is swung upwardly or downwardly about pivotmember 16.

Arm assembly 10 further includes a locking mechanism generallydesignated at 30 (FIGURE 2) which is designed to prevent arm assembly10' from pivoting downwardly about pivot member 16 by preventing therelative axial movement between members 12 and 14 which normally wouldoccur when downward pressure is: exerted on the arm assembly. As shownin FIGURE 2, locking mechanism 30 includes a spring retainer 32 fixed toparallel member 12 by any suitable means, such as screws 34. Theretainer has a pair of downwardly depending legs 36 which straddlemember 14. A coil spring 38 disposed about member 14 has one end 40seated in a spring guide 42 which in turn is supported against thedownward depending legs 36 of spring retainer 32. The coil spring hasits other end 44 seated in a spring guide 46 which is therebyresiliently urged toward a stop 48 fixed to member 12 by any suitablemeans such as screws 50. Stop 48 includes a pair of downwardly dependinglegs 52 which straddle member 14, each leg having an inclined camsurface 55 thereon for purposes set out hereinbelow.

Slidably carried by parallel member 14 are one or more locking discs 54and a latch '56. Each locking disc 54 and the latch 56 has a sharp edgedopening 62 therethrough to permit the passage of member 14. As viewed inFIGURE 2, the letters A, A and A" are used to designate the rearward orleft hand edges of openings 62 and the letters B, B and B" are used todesignate the forward or right hand edges. In addition, latch 56 iscounterbored at which makes the latch and locking discs 54 movable intoeither of two positions; a first or upright position wherein the latchand locking discs are slidable with respect to member 14 and a second orinclined position (as shown in FIGURE 2) wherein the latch and lockingdiscs are inclined on member 14 so that sharp edges A, A, A", and B, B,B" frictionally engage parallel member 14. It should be apparent thatwhen locking discs 54 and latch 56 are in the first position, members 14can move axially with respect to member 12 by sliding through openings62. However, with locking discs 54 and latch 56 in the second orinclined position and sharp edges A, A, A, and B, B, B" frictionallyengaged with member 14, member 14 is prevented from moving axially withrespect to member 12 in a manner and for purposes set out hereinbelow.

Moving locking discs 54 and latch 56 into the second or inclinedposition is accomplished by coil spring 38 which urges the discs andlatch against inclined cam surface 55 of stop 48. As set forthhereinabove, when arm assembly 10 is moved downwardly, parallel members12 and 14 will move axially one relative to the other. For example, asshown in FIGURE 2, member 14 will tend to move axially with respect tomember 12 in the direction indicated by arrow 63. Since locking discs 54and latch 56 have their sharp rearward or left hand edges A, A and A"frictionally engaged with member 14, the locking discs and latch arealso carried in the direction indicated by arrow 63. Stop 48, however,prevents forward movement of locking discs 54 and latch 56, which inturn prevents further movement of member 14 in the direction indicatedby arrow 63. In this manner, member 14 is prevented from moving axiallywith respect to member 12 which in turn prevents arm assembly 10 frompivoting downwardly about pivot member 16. The greater the downwardpressure exerted on arm assembly 10, the more forceful will be theengagement between sharp edges A, A and A and member 14 to keep theassembly from lowering. However, when upward pressure is applied toassembly 10, member 14 tends to move axially away from stop 48 in thedirection indicated by arrow 65, and toward the resilient support ofcoil spring 38. Since locking discs 54 and latch 56 have their sharpforward or right hand edges B, B and B" frictionally engaged to member14, the locking discs and latch are also carried toward the resilientsupport of coil spring 38. By moving against the resilient support ofthe coil spring, the locking discs and latch are carried to the first orupright position on member 14 which restores the sliding relationshipbetween locking discs 54, latch 56 and member 14. Thus, as upwardpressure is applied, member 14 is able to move axially in the directionindicated by arrow 65 with respect to member 14 which in turn allows thearm assembly 10 to pivot upwardly about pivot support 16. Arm assembly10 will continue to move upwardly until it is released. At this pointthe assembly will begin to fall by gravity causing sharp edges A, A andA of looking discs '54 and latch 56 to re-engage member 14 whichprevents arm assembly from pivoting downwardly in a manner as set outhereinabove.

In order to disengage locking mechanism 30 for moving the arm assemblydownwardly, latch 56 is provided with an upper portion 66 which extendsthrough member 12 terminating in a knob 68. Using the downward dependinglegs 52 of stop 48 as a fulcrum, depressing knob 68 causes the latch andlocking discs to pivot to the first or upright position on member 14.This restores the sliding relationship between the locking discs, latchand member 14 which permits member 14 to move axially with respect tomember 12 in the direction indicated by arrow '63. This in turn allowsthe arm assembly to pivot downwardly about pivot support 16. When thedesired lower level is reached, knob 68 is released which instantlyactivates locking mechanism 30 to prevent the arm assembly from furtherdownward movement as set forth hereinabove.

Therefore, it will be appreciated that the present in ventionaccomplishes its intended objects. The parallel motion or linkage ofmembers 12 and 14 provides a simple low cost arrangement for maintaininginstrument tray 22 in a horizontal position regardless of: theinclination of arm assembly 10. Furthermore, locking mechanism 30prevents downward movement of the arm assembly while permitting theassembly to swing upwardly at the slightest upward pressure.

This one way action of the locking mechanism acts as a safety feature toprevent possible injury to the patient or equipment when the dentalchair is elevated with the arm and instrument tray extended over thepatient. In this respect, the arm will yield and ride up with thepatient under the influence of upward pressure exerted by the patient onthe arm. The arm will continue to ride up with the patient until theupward pressure is removed at which point the arm will automaticallylock against downward movement. Furthermore, if the dentist desires toraise the arm, he can do so without unlocking the friction lock simplyby lifting the arm to the desired level. The arm when released, willthen automatically lock at this level. Moreover, since the surface ofparallel member 14 is free of any obstruction, there being no setstations for sharp edges A, A, A" or B, B, B" to engage, the latch andlocking discs can engage member 14 at any point along the length of themember so that the arm assembly can be positioned and maintained at anylevel.

While I have described the preferred embodiment of my invention, it willbe readily apparent that various modifications can be made thereinwithout changing the spirit and scope of the invention. Having thusdescribed my invention in detail, what I claim as new is:

1. A movable supporting structure for supporting an object in adjustedposition comprising:

(a) a parallel motion linkage having first and second parallel membersmovable axially, one relative to one another, the parallel members beingpivotally supported at one end and pivotally connected to said object attheir other end;

(b) a plurality of sharp edged elements slidably mounted on said firstparallel member;

(0) means for causing said sharp edged elements to frictionally engagesaid first parallel member including a stop attached to said secondparallel member and having a surface inclined at an angle to saidparallel members for tilting said sharp edged elements causing the sharpedges thereof to frictionally engage said first parallel member; and

(d) means for releasing the frictional engagement of said sharp edgedelements and said first parallel member.

2. A movable supporting structure as set forth in claim 1 furthercomprising means resiliently urging said sharp edged elements intocontact with the inclined surface of said stop means for tilting saidsharp edged elements.

3. In combination with a parallel motion linkage hav ing two parallelmembers movable axially one relative to another, the parallel membersbeing pivotally supported at one end and pivotally connected to anobject at their other end, a friction locking device for maintaining theobject in a vertically adjusted position comprising:

(a) a member having a surface inclined with respect to one of saidparallel members rigidly mounted on a second of said parallel members;

(b) locking elements slidably mounted on said one parallel member, eachof said locking elements having a sharp edged opening therethrough topermit the passage of said one parallel member; and

(c) resilient means urging said locking elements against said inclinedsurface for tilting said locking elements on said one parallel memberand frictionally engaging said one parallel member with the sharp edgesof said openings to prevent said parallel members from moving axiallyone relative to another whereby said parallel members are prevented frompivoting downwardly for maintaining said object in a vertically adjustedposition.

4. The combination as set forth in claim 3 in which said resilient meanscomprises:

(a) a spring retainer rigidly fixed to said second parallel member; and

(b) a spring biased against said spring retainer and toward the inclinedsurface of said member.

5. The combination as set forth in claim 4 in which said spring isdisposed about said one parallel member.

6. The combination as set forth in claim 3 in whic said locking memberscomprise:

' (a) a plurality of disc-shaped elements each having a sharp edgedopening therethrough and each slidably carried by said one parallelmember; and

(b) a latch disposed between the inclined surface of said member andsaid discs, said latch having a sharp edged opening therein counterboredto permit said latch to tilt with respect to said one parallel memberfor moving said latch and disc shaped elements into said tilt position.

7. The combination as set forth in claim 6 in which said latch has ahandle portion for manually moving said latch and therefore saiddisc-shaped elements against said resilient means and away from theinclined surface of said member to permit said parallel members to moveone relative to another, whereby said parallel members pivot downwardly.

References Cited UNITED STATES PATENTS ROY D. FRAZIER, Primary Examiner.

U. FRANKLIN FOSS, Assistant Examiner.

US. Cl. X.R. 21 1-100

